There has been a strong demand for saving of the air-conditioning cost of buildings by preventing an increase of the inside temperature caused by the solar rays, for reducing the evaporation loss of volatiles from oil tankers, natural gas transport ships, and tanks installed on land by coating the outer surface of these facilities and for improving refrigerating efficiency of tanks and home electrical appliances. For example, the loss of crude oils by evaporation from tankers is enormous and it is said to amount to 0.2 to 0.5% of the total load in one voyage from the Near East or the Middle East to Japan.
To deal with the above-mentioned problems, white pigments such as titanium oxide and colored pigments have hitherto been used in solar heat-shielding coatings. Coloring in white produces a solar heat-shielding effect to some extent, but coloring in other than white leads to a marked reduction of this effect. In consequence, there is a demand for availability of coating compositions in any desired color of a good solar heat-shielding effect.
On the other hand, aluminum paints containing scaly aluminum powders have been known as solar heat-shielding coatings for the roofs of buildings and the outer surface of tanks. These paints are available in a limited number of colors and do not possess sufficient durability and, besides, they are not suitable for the places to be walked on because of their poor abrasion resistance.
Heat-reflective enamels containing antimony trioxide, antimony dichromate, alkali metal dichromates and the like are proposed in Japan Kokai Tokkyo Koho No. Sho 56-109,257 (1981) to solve the above-mentioned problems. They are, however, not desirable from the viewpoint of environmental sanitation as they contain heavy metals.
Processes for the manufacture of metal plates covered with emulsion coatings containing fine glass powders with a particle diameter of 20 to 350 .mu.m, coatings containing synthetic silica powders and white pigments with a particle diameter of 300 .mu.m or less or coatings containing ground glass with a particle diameter of 5 to 300 .mu.m are proposed in Japan Tokkyo Koho No. Sho 55-33,828 (1980) and Japan Kokai Tokkyo Koho Nos. 55-120,669 (1980) and 55-74,862 (1980). Theses coatings exhibit an excellent solar heat-shielding effect in the initial stage, but they suffer a marked loss of this effect with the passage of time as they have an uneven texture on their surface and show poor long-term antisoiling properties. Hence, it was difficult for this type of coatings to be safe and colorable in any desired color and to maintain the solar heat-shielding effect for an extended period of time.
Such being the case, the present inventors already proposed in Japan Kokai Tokkyo Koho No. Hei 1-121,371 (1989) that (1) one or more of zirconium oxide, yttrium oxide and indium oxide and (2) compounds of one or more of zirconium oxide, indium oxide, titaniumm oxide and silicon oxide and one or more of magnesium oxide, yttrium oxide, barium oxide, calcium oxide and zinc oxide are substances capable of meeting the above-mentioned property requirements.
The present inventors also proposed in Japan Kokai Tokkyo Koho No. Hei 1-263,163 (1989) to use Si or an alloy or alloys of Si and one or more of Al, Fe, Mg, Mn, Ni, Ti, Cr and Ca with a particle diameter of 50 .mu.m or less as solar heat-shielding pigments for achromatic gray such as Munsell color notation N-2 to N-7. Moreover, they proposed the use of colored pigments based on complex oxides for chromatic color in Japan Kokai Tokkyo Koho No. Hei 2-185,572 (1990). The technologies thus disclosed have made it possible to provide compositions and structures with solar heat-shielding effects for white, achromatic gray, and chromatic color. Coloring in black for which the largest effect is expected, however, requires the use of carbon black, iron black, copper chrome black and the like and this was bound to lower the solar heat-shielding effect.
It is an object of this invention to provide a black coating composition which covers the surface of a variety of structures on land and sea, ships, buildings, and home electrical appliances exposed to direct solar rays to prevent a rise of the inside temperature thereby reducing the air-conditioning cost or loss by evaporation of the contents for a marked saving in energy and is serviceable with long-term durability, free of problems relating to environmental sanitation, and of good appearance and to provide a structure coated therewith.